Self-sealing fuel tank



Aug. 12, 1947. P. J. DAsHER Er Al.

SELF- SEALING FUEL TANK Filed Aug. l16, 1940 Patented Aug. l2, 1947 1 ny. UNITED s'rli'rss PATEN orrlcs SELF-SEALING FUEL TANK Paul J. Dasher,Stow, Richard A. Crawford,

' Akron, and Russell S. Colley, Kent, Ohio, as-

signors to The B. F. Goodrich Company, New York, N. Y., a corporation ofNew York Application August 16, 1940, Serial No. 352,900

9 Claims.' (Cl. 154-435) This invention 'relates to self-sealing tankssuch as gasoline tanks for airplanes which must not be permitted to leakeven after puncture by small arms projectiles.'

Constructions heretofore proposed for preventing leakage from perforated-fuel tanks have suffered from a number of disadvantages, such asfailure to seal the large jagged hole left at the exit of a projectilefrom the tank, and loss of large volumes of fuel by absorption in thesealing layer or by fiow into spaces between a perforated tank and asealing covering. Previously known constructions have accordingly notmet the need for a container which will not lose its forcement, inContact with the contents of the tank, a relatively thick sealing layer,and an outer skin. If the tank is to be filled with a liquid other thangasoline, such as a hydrocarbon oil, the materials used will be such aswill have the desired properties when in contact with the liquid.Because it is not completely rigid, it is ordinarily preferred toenclose this composite` tank completely, except for the necessaryinlets, outlets and other connections, 'by a rigid supporting structure,in which it fits snugly without free spaces or wrinkles.

The inner gasoline-resistant layer may be a foil such as Cellophane ormetal foil or any of the various flexible gasoline-resistantcompositions` possessing the requisite strength and resiliency over therange of temperatures encountered in aviation service, such aspoly-ethylene polysulde, polyvinyl alcohol plasticized with glycerine orthe like, polyvinyl chloride plasticized ywith gasoline-insolublearomatic liquids, neoprene (polymerized chloroprene), or the rubberycopolymer of butadiene and acrylonitrile, and preferably ,the latter,although neoprene is quite satisfactory for fuels substantially freefrom aromatic compounds. Such compositions, when properly prepared, arequite resistant to tear, es-

pecially when reinforced by a Isuitable fabric,

and promptly close behind a projectile which pierces them.

The sealing layer should exhibit sucient strength and resilience topermit yield of the material and recoveryafter rupture by projectilesWithout appreciable loss of any material, and should swell rapidly whenin contact with gasoline, but should not dissolve appreciably in thegasoline. One such material is ordinarilyvulcanized soft rubber. Amaterial which has the special advantage of-very light weight for agiven volume-is closed-cell sponge rubber, and especially Aug-ust 3,1940) typical examples being mixtures of rubbery polyisobutylene withvulcanizable rubber or synthetic rubberl which is then vulcanized, ormixtures of unvulcanized rubber with a material such as the rubberycopolymer of butadiene and acrylonitrile which is gasoline-resistanteven when unvulcanized, or even mixtures of unvulcanized rubber withneoprene, the neoprene alone being vulcanized. Appreciable proportionsof each of the two types of ingredients must be present in order thatthe desired properties may be manifested and preferably neither oneshould greatly exceed three times the quantity of the other. i V

It is not essential that the sealing layer be made throughout of asingle material, `for it is possible and sometimes advantageous to makedifferent portions of it of different' materials or even to subdividethe total thickness of the sealing layer into a plurality of portionsand interpose other materials of any of the three types, namely,gasoline-impervious,y or sealing material, or tough skins. f

The outer skin may be any material of high `tear resistance and fairlyhigh tensile Ystrength such as vulcanized sheet rubber or syntheticrubber, fabric or rubberized fabric, felt, leather or the like.

The supporting" structure should be suiciently strong to support severaltimes the weight of the contents of th'e tank so as to resist the surgesand centrifugal forcesarising as a result of the maneuvers of thesupporting vehicle. The material in direct contact with the tankstructure should be of such a nature asnot to produce jagged splintersor exfoliations when pierced or fractured. If metal, it should be aductile vmetal of moderate thickness which exhibits only a smallprojecting ridge when pierced by a projectile. In

` mairv cases the tank will be located in otherwise Such illlers may beof even-grained wood such as e white pine but are preferably of a veryvlight weight material which is rigid butv somewhat resil-` 'ient sothat large fragments do not tend to break out of it wh'en pierced, suchas balsa wood, hard rubber sponge, cork blocks and the like,

'I'he total thickness of the composite tank struc ture must at leastapproximate the diameter of the projectile the tank is likelyv toencounter. Small arms projectiles are ordinarily pointed, and are firedfrom a rie s'o that they enter pointed end first, leaving a clean holeat the point of entrance, with mainly lateral displacement and onlyslight exfoliation of metals which are pierced, and only slight fractureor splintering of wood. Such irregularities as are produced'in thesupporting structure at the point of entrance are therefore of smallermagnitude th'an thickness of the sealing layer and are accommodated inthe outer zones of the resilient sealing layerwithout producing sucientdistortion to hold open the hole through the tank wall. In entering thetank, the projectiles are usually deected sumciently that they leave thetank sidewaysor while tumbling end over end and consequently make alarge, jagged hole in the supporting structure at the point of exit,with' pronounced splinters and exfoliations extending in the directionof travel of the projectile, but since this direction is away from-thetank wall such projections can do no harm and will not hold open any`holes in thevv sealing layer as would be the case if the sealing layerwere outsideof a metal tank. Care must be taken to avoid any adhesion ofthe tank to the'supporting structure, else any deformation of thesupporting structure would tend to hold open holes in the tank wall andpermit leakage.

If the course of th'e projectile is through the body of liquid in thetank, the projectile produces in the liquid ahead of it a pressure cone.It' the tank' wall is not adequately supported this high local pressurewill bulge the tank wall so that the' passage of the projectile producesnot simply a small hole but a large tear. It is therefore important thatthe outer surface of the tank wall be in close contact throughout itsextent with' a supporting structure of adequate strength and rigidity.Furthermore, in order to minimize the extent of'tearing which may resultfrom perforation of the tank after partial destruction of the supportingstructure, it is important that both surfaces of the tank wall, andparticularly the outer surface, resist tearing to as great an extent aspossible.

When s mall arms projectiles'are fired through a, tank' constructed inthe manner outlined above. they produce only small displacements of thesupporting structure at th'e point of entrance,

and the more extensive displacements at the point i I4 is of such sizeas Just to fit snugly against its of exit'extend away from the tank anddo. ynot affect the tank itself. The Aholes through the tank wallimmediately close behind the projectile because of the resiliency of thematerials used. Any

slight seepage which may occur through the inner l ,tank surfacewillcome in contact with th'e sealing Fig. 1 represents a cross-sectionof an airplane 'n wing tank in place;

Fig. 2 is a fragmentary section of the tank wail on .an enlarged scale,and

Figs. 3 and 4 'are similar sections of tank wall constructions.

In Fig. 1 the metal surface I0 of an airplane wing is provided withreinforcing stringers II, II. Th'e central portion of the inside of thewing, which is to be occupied by the tank, is set oflby partitions I2,I2 which may be made of metal and which'serve as lateral supports forthe tank. The spans between the stringers II are filled in with slabs I3of balsa wood so as to'provide a flat bed for the vertical support ofthe tank. The tank valternative supporting surfaces.

e tank Il, as shown in Fig. 2, ismade up of an inner gasoline-resistantlayer I5 of a vulcanized copolymern of butadiene and acrylonitrile, inwhich-is embeddeda strong, tear-resistant fabric I6 such as,24 oz. duck,the thickness of the layer |15 outside the fabric being about .07 inch.Adhered to the layer I5 is a sealing layer I1 about .20 inch thick, of amixture of about equal parts of unvulcanized rubber and of anunvulcanized rubbery copolymer of butadiene 5565% and acrylonitrilef5-35%, to which may `be added, if desired, a plasticizer forthe-copolymer such as dibutyl phthalate in an amount up to aboutone-fourth the weight of the copolymer. This sealing layer, because ofits rubber contentl will swell when brought into direct contact withgasoline, but, because of its content of the copolymer, which isinsoluble in gasoline and thoroughly intermingled with the rubber, itwill Vnot dissolve appreciably, and because it is unvulcanized itremains sufciently plastic and self-adherent1 under ordinary conditionsto minimize danger.

ance to tear, hence it is advantageous to make 'it f of a rubbercomposition 4containing reinforcing pigments such as carbon black andvulcanized with the aid of accelerators free from tendency to overcuresuch as the mercaptothiazoles and their derivatives, as will be wellunderstood by rubber technologists.

A fuel tank so constructed may be pierced by y an almost indefinitenumber of .30 caliber machine gun bullets and even by a considerable'.

number of .50 caliber bullets with little or no leakage, and such leaksas do appear almost always close very soon as aresult of the swellin ofthe sealing layer Il by the gasoline.

In the modication shown in Fig. 3, the plastic sealing layer Il occupiesonly part of the space between the lining I5 and the outer skin I8, theremainder being made up of closed-cell vgas-expanded rubber I9, whichmay be either inside or outside of the layer Il but preferably cut-1side as shown. This construction has the advantage of considerablylighter weight for a -given thickness, and combines the self-sealingqualities of the plastic il, with the ability of the compressible layeri9 to accommodate irregularities which may be produced by perforation ofthe supporting structure. A still further saving in weight may beeffected. by omitting the' plastic and making the entire sealing layerof the closed-cell gas-expanded rubber I9, as is shown in Fig. 4, inwhich case the layer I9will tend to close any periorations by swellingin the gasoline, although it will lack the self-adherence of the plasticcomposition Il.

It is to be understood that the embodiments herein specically describedare illustrative and that equivalents may be substituted as has beenfully pointed out above.

We claim:

1. A self-sealing flexible tank comprising a lining ofgasoline-impervious vulcanized synthetic rubber-like material, a rubberysealing layer which will swell in gasoline but will not4 dissolve ingasoline, and a tough, tear-resistant outer skin, all adhered together.

2. A self-sealing iiexible tank comprising a gasoline-imperviousresilient lining, a sealing layer of a mixture including a rubberymaterial which swells in gasoline with a rubbery material which isinsoulble in gasoline, and a. tough, tear-resistant outer skin, alladhered together.

3. A self-sealing flexible tank comprising a gasoline-imperviousresilient lining, a composite sealing layer including a. mixture of arubbery material which swells in gasoline with a rubbery material whichis insoluble in gasoline and a cled-cell gas-expanded sponge rubber, anda tough, tear-resistant outer skin, all adhered t0- a. A self-sealingtank comprising a exible container having a gasoline-impervious.-lining, a rubbery sealing layer which will swell in gasoline but willnot dissolve in gasoline, and a tough,-

tear-resistant outer skin, all adhered together, and a rigid supportingstructure in contact with the outer skin throughout its extent.

5. A' self-sealing tank comprising a flexible container having agasoline-impervious lining ofk a vulcanized synthetic rubber-likematerial, a rubbery sealingy layer which will swell in gasoline but will.not dissolve in gasoline, and a tough, tear-resistant outer skin, alladhered together, and an irregular supporting structure, theirregularitiesv of which are -lledin by rigid porous nllers so that thetank is in direct contact with but hott adhered to a substantiallysmooth solid suppo v l l o. A self-sealing `tank comprising a nexiblecontainer having a gasoline-impervious lining of a vulcanized syntheticrubber-like material, a sealing layer of a Vclosed-cell gas-expandedL`sponge rubber; and a tough, tear-resistant outer skin, all adheredtogether, and an irregular supporting structure the irregularities ciwhich are filled in by rigid porous fillers so that the tank is indirect contact throughout its extent with a substantially smooth solidsupport.

7. .A self-sealing tank comprising a ilexible container having agasoline-irripervious resilient lining of a vulcanized copolymer ofbutadiene and acrylonitrilehaving a fabric reinforcement, a'

sealing layer of a mixture of av rubbery material which swells ingasoline with a gasoline-insoluble rubbery copolymer of butadiene andacrylonitrile, and a tougli,` tear-resistant outer skin, all adhered'together, and an irregular metallic supporting structure, theirregularities of which are filled in by balsa wood llers so that thetank is in direct contact throughout its extent Vwith a vsubstantiallysmooth solid support.

8. A self-sealing tank comprising a exible container having animpervious lining, a rubbery sealing layer and a tough, tear-resistantouter skin, all adhered together, and a rigid supporting structure incontact with the outer skin throughout its extent but not adhered toit.

9. A self-sealing tank comprising a flexible container having vagasoline-impervious lining, a

.rubbery sealing layer which will swell in gasoline but will notdissolve in gasoline, and a tough, tear-resistant outer skin, alladhered together, and a rigid supporting structure in contact with theouter skin throughout its extent but not adhered toit.

PAUL J. DASHER.

RICHARD A. CRAWFORD? RUSSEIL S. COILEY.

REFERENCES CITED lThe following references are of record in the ille ofthis patent:

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